1. Field of the Invention
This invention is related to relief devices, including pressure relief devices and vacuum relief devices; to equipment or storage tanks with fluid therein under pressure with such devices; and, in one particular aspect to a gas relief device in which a fluid under pressure opposes pressure of a stored fluid to inhibit leakage of the stored fluid.
2. Description of Related Art
Fluid relief devices are widely used to prevent undesirable over or under pressures (excess or insufficient) of fluid stored in storage tanks or in other equipment when abnormal conditions exist. During normal operating or storage conditions, a weight or other method of loading typically forces a cover against a seal to prevent fluid under pressure in the storage tank or equipment from escaping through the relief device. An environmental concern with these devices is that there is typically an amount of leakage of the stored or contained fluid through or past the relief device seal even under normal conditions.
The prior art discloses a variety of storage systems and leakage detectors. U.S. Pat. No. 4,912,966 discloses a storage tank system and an inner tank, an outer jacket, an air pressure or vacuum means located in the space between the inner tank and the outer jacket. Leak detection apparatus is provided.
U.S. Pat. No. 3,902,356 discloses a storage tank having a bottom, a separating bottom, gas-filled space between the bottom and the separating bottom, and a differential pressure leakage indicator gauge.
U.S. Pat. No. 4,478,178 discloses an enclosure having spaced pressure relief valves, and a gas-filled chamber positioned between the two relief valves.
U.S. Pat. No. 5,046,354 discloses a pressurized storage tank having a shut-down valve assembly.
U.S. Pat. No. 3,848,765 discloses a double-walled tank and means for ascertaining when any liquid enters the space between an inner tank and an outer tank.
German Patent 3,933,265 discloses a leakage detection system for a multiple-walled pressure container.